Yes of course weight plays a big role as does wetted surface and you've removed a fair amount of that but don't ever think that with adequate sail area that you can't get your boat moving well. Steel is not the best choice in boats under 40 feet because of the weight but you sleep well knowing whatever you might hit will come out second best. It won't be a speed ball but if you get some sail up you can still make decent passage times. The Cape George 31 is a boat of similar weight and it does excellent passages in the trades but in can set quite a bit of sail. A good sized drifter and a poled out genoa on the opposite side will give you a decent spread.

The Hasler vane is pretty much identical to the Aries and other servo pendulum vanes except the wind vane has a vertical pivot on the Hasler vice the horzontal pivot on the Aires, et al. The horizontal pivot was found to be more sensitive but the Hasler worked fine. Believe it was more of a cost issue and motivation to be a vane builder instead of a sailor that lead to the Hasler's demise.

If you have a boat that is directionally stable and the sail plan balanced, a vane will steer down to knot or less. My current boat's vane is only limited by having enough wind to deflect the vane at something well under 5k relative wind. The faster a boat goes, the more power a servo pendulum generates. Believe it's more a problem of the friction in a wheelsteering system than issues with the vane that hurt there low wind/low speed steering.